The invention relates to a self-adjusting equalizer configuration which automatically adjusts to the cable length. The equalizer configuration includes a band limitation for the transmission of digital signals and consists of an equalizing amplifier, a correction filter, and an amplitude control loop which includes a comparison of actual and nominal values.
Digital signal regenerators in transmission systems with coaxial cables as the transmission medium have an automatic attenuation equalizer at the input in order to equalize the distortions resulting from the frequency-dependent cable loss. The amplitude of the equalized signal; e.g., the amplitude of the signal at the discriminator, is used as a control criteria for adjusting the equalizer to the length of the cable. This pulse amplitude must be as independent as possible from the input pattern. However, this is the case only when a specific band limitation is adhered to in the equalizer. To suppress random noise and interference signals, however, a tighter band limitation must be used which results in varying pulse amplitudes in the signal path as a function of the input pattern.
The band limitation required to reduce noise is usually implemented as a "roll-off" band limitation as described, for example, in the book by P. Bocker: "Datenuebertragung" (Data Transmission), Vol. 1, pages 98-114 (Springer Verlag 1978).
Transmission systems for higher bit rates, such as 34 Mbit/s, are only possible with a roll-off factor that is less than 1 for the field lengths and transmitting power applicable in this case, so that r&lt;1. This fact results in signal overshoots, the amplitude of which is dependent on the pulse sequence. This concept will be explained later with reference to FIG. 1. Another known configuration that circumvents the disadvantage of the dependence of the equalizer setting on the pulse sequence will be explained with reference to FIG. 2. The difficulties that are particularly evident for this configuration are explained as follows: The maximum gain of the equalizing amplifier for a roll-off factor with the value 1 is greater and takes place at a higher frequency than that of an amplifier for a roll-off factor with a value &lt;1. This is illustrated in FIG. 7 and requires more effort, particularly at higher bit rates such as 140 Mbit/s. In addition, two phase-equalized filters are located in the signal path, the tolerances and aging of which directly influence the accuracy, and therefore the quality, of the regenerator.